The plastic analysis of structures is easy and straightforward for simple structures, the
complete study could be done manually. Once the structure is more than one span and one
level, the problem gets worse and the determination the collapse load and the collapse
mechanism becomes more complicated and requires the use a digital program or calculation
software.
In the present work, a numerical program in Matlab using the finite element method for
successive linear analysis has been developed for the load factor calculation by adopting the
approach of first-order plastic hinges. The program is based on step by step method and is
developed by adopting the theory of plastic hinges as an approach to determine the collapse
load and the collapse mechanism of such structures in flexure and considering the interaction
of bending moment and axial force. The program has the ability to generate interaction
diagrams for frames of more than one level and more than one span. This permits the
prediction of the nature failure mechanisms depending on the ratio between concentrated
vertical loads, V, and horizontal loads, H (α=V/H). The approach used in the present work has
been found in a good agreement with the limit analysis for the determination of the true
failure load factor and the mechanism corresponding. The approach is very similar with the
principal of virtual work method for the construction of interaction diagrams, V-H.